Turbocharged and supercharged engines may be configured to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, an intercooler or charge air cooler (CAC) may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Low pressure exhaust gas recirculation (EGR) can further increase the condensate amount in the CAC by increasing water vapor concentrations and hence, increasing the temperatures at which condensation can occur. Condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. Under certain air flow conditions, condensate may exit the CAC and enter an intake manifold of the engine as water droplets. If too much condensate is ingested by the engine, engine misfire and/or combustion instability may occur.
Other attempts to address engine misfire due to condensate ingestion include avoiding condensate build-up. In one example, the cooling efficiency of the CAC may be decreased in order to reduce condensate formation. However, the inventors herein have recognized potential issues with such methods. Specifically, while some methods may reduce or slow condensate formation in the CAC, condensate may still build up over time. If this build-up cannot be stopped, ingestion of the condensate during acceleration may cause engine misfire. Additionally, in another example, engine actuators may be adjusted to increase combustion stability during condensate ingestion. In one example, the condensate ingestion may be based on a mass air flow rate and amount of condensate in the CAC; however, these parameters may not accurately reflect the amount of water in the charge air exiting the CAC and entering the intake manifold. As a result, engine misfire and/or unstable combustion may still occur. Further still, some systems for estimating water accumulation within the CAC may only be accurate when EGR is off (e.g., not flowing) since EGR may introduce additional moisture into the charge air.
In one example, the issues described above may be addressed by a method for adjusting engine actuators based on water storage at a charge air cooler (CAC), the water storage based on an output of an oxygen sensor positioned downstream of the CAC, ambient humidity, and exhaust gas recirculation (EGR) flow. Specifically, the oxygen sensor may be positioned at an outlet of the CAC. An engine controller may use the output of the oxygen sensor to determine water content of the charge air exiting the CAC. The water content of the charge air entering the CAC may be estimated by ambient humidity plus water content of EGR (e.g., low-pressure EGR) entering an intake passage upstream of the CAC. The water content of the EGR may be based on the amount of water vapor in the exhaust gases and the amount of exhaust gases flowing into the intake passage (e.g., the EGR flow). The EGR flow may be determined from an EGR flow measurement sensor (such as a DPOV sensor) positioned in the EGR passage. In one example, the ambient humidity may be measured by a humidity sensor positioned upstream of the CAC and the EGR passage. The difference between the water content of the charge air entering the CAC and the water content of the charge air exiting the CAC may then be indicative of a water storage rate (e.g., water accumulation rate) within the CAC. The engine controller may then adjust engine operation to increase combustion stability, decrease condensate formation in the CAC, and/or evacuate condensate from the CAC in response to the determined water storage rate (or amount). As a result, condensate formation within the CAC may be reduced and engine misfire and combustion instability due to water ingestion may be decreased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.